Enzyme assays are used to measure enzymatic activity, which is a measure of the quantity of active enzyme present in a reaction. Enzyme assays are important when analyzing enzyme kinetics and enzyme inhibition. Enzyme kinetics relates to chemical reactions that are catalyzed by enzymes. In enzyme kinetics, the reaction rate is measured and the effects of varying the conditions of the reaction investigated. Enzyme kinetics reveal the catalytic mechanism of an enzyme, its role in metabolism, how its activity is controlled, and how a drug or a poison might inhibit the enzyme.